Imaging systems are frequently used in automotive systems to provide imaging of the roadway around the vehicle. In the case of frontal images, the images provided by the imaging systems are often used by other systems, such as lane tracking systems, adaptive cruise control systems, or other systems. The function of these system depends, at least in part, on the quality of the images acquired by the imaging system.
In order to implement imaging systems for automotive applications that involve imaging outside the vehicle, several issues need to be addressed. One such issue relates to maintaining a clean optical path between the scene to be imaged and the imaging system itself. Many implementations make use of the existing optical cleaning systems afforded by vehicle windshield wipers that are used to help maintain a driver's vision clear. Such systems place the image-sensing component inside the vehicle, such that it “looks” out through the windshield in a region that is swept clean by the windshield wipers.
Typically, such an implementation would involve a location near the top of the windshield, in the center of the vehicle. The resulting geometry tends to reduce the amount of light that passes through the system to the imaging or detector, and the physical mounting of the imaging system becomes very cumbersome and bulky. Further, such a placement frequently results in the placement of the sensor system, in some cases, nearly parallel to the windshield. As shown in FIG. 1A, the portion of the inside of the windshield (10) through which the light impinging upon the sensor (12) passes, i.e. that portion of the windshield that must be kept clean in order for the sensor to function properly, combined with the area of the windshield obstructed by the camera itself becomes relatively large.
In attempts to minimize this accumulation of contaminants, some systems make use of an optically opaque boot or enclosure to completely enclose the optical path within the vehicle and isolate it from the rest of the vehicle passenger compartment. Such enclosures tend to further increase the apparent bulk of the imaging system implementation.
Other optical systems make use of mirrors. One such example includes external rearview mirrors. These mirrors are located in protrusions that extend outside of the vehicle. These protrusions limit the aerodynamic efficiency of the vehicle. Further, many attempts have been made to reduce or eliminate the protrusions for aesthetic reasons.